The dwarf sperm whale is similar in appearance to the pygmy sperm whale, but has a larger dorsal fin (5% of the body length), generally set nearer the middle of the back. Like its congener, the dwarf sperm whale has a shark-like profile (but with a more pointed snout than the pygmy sperm whale).

Dwarf sperm whales have grey (dorsal) to white (ventral) colouration, and a pigment marking shaped like a shark's gill slit on the side of its head. Generally, a pair of short grooves, similar to those in beaked whales, is present on the throat.

There are 8 to 11 (rarely up to 13) pairs of teeth in the lower jaw; sometimes teeth are present in the upper jaw as well.